Two-Axis Electromagnetic Microscanner for High Resolution Displays

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Two-Axis Electromagnetic Microscanner for High Resolution Displays Arda D. Yalcinkaya, Hakan Urey, Dean Brown, Tom Montague, and Randy Sprague

Abstract—A novel microelectromechanical systems (MEMS) actuation technique is developed for retinal scanning display and imaging applications allowing effective drive of a two-axes scanning mirror to wide angles at high frequency. Modeling of the device in mechanical and electrical domains, as well as the experimental characterization is described. Full optical scan angles of 65 and 53 are achieved for slow (60 Hz sawtooth) and fast (21.3 kHz sinusoid) scan directions, respectively. In combination with a mirror size of 1.5 mm, a resulting opt product of 79.5 deg mm for fast axis is obtained. This two-dimensional (2-D) magnetic actuation technique delivers sufficient torque to allow non-resonant operation as low as dc in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies large enough to support SXGA (1280 1024) resolution scanned beam displays. [1653]

I. INTRODUCTION CANNED light beams are used to produce display images for a wide variety of applications, including such applications as automotive head-up displays and head-worn displays [1]–[4]. A mirror producing angular motion is used to deflect a modulated light beam on an image plane to create a display. In order to construct a two-dimensional (2-D) rasterlike rectangular image, the mirror is rotated about two orthogonal axes at different frequencies. High performance microelectromechanical systems (MEMS)-based display design is a very challenging work. The scanner represents the system’s limiting aperture, requiring a sufficient size. Besides, the mirror flatness of fractions of a wavelength has to be realized so as not to distort the beam’s wave front. The scan frequency has to be high enough to handle the many millions of pixels per second. Two-axis scan over significant angles has to be performed in order to paint a wide angle, 2-D image. Using the presented new actuation method, MEMS scanner designs have been implemented satisfying the requirements of a variety of display and imaging applications. This paper describes modelling and characterization of a novel high performance 2-D MEMS scanner for display applications. The presented device uses mechanical coupling of the outer frame motion into the scan mirror. The outer frame is actuated in two axis using an electromagnetic torque, created by a single coil interacting with an external magnet placed at 45 to the orthogonal axis. This novel actuation technique

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Manuscript received July 9, 2005; revised November 14, 2005. Subject Editor N. C. Tien. A. D. Yalcinkaya and H. Urey are with the College of Engineering, Koç University, TR 34450 Istanbul, Turkey. D. Brown, T. Montague, and R. Sprague are with Microvision, Inc., Bothell, WA 98011 USA. Digital Object Identifier 10.1109/JMEMS.2006.879380

Fig. 1. Conceptual optics of the retinal scanning beam display (RSD). The final image on the retina is a 2-D raster pattern.

allows producing large scan angles at low actuation powers due to high mechanical quality factors obtained in air. Since there is no direct electrical or mechanical loading on the scan mirror, exceptionally high quality factors are obtained in air. Another strength of the device is to use single coil, single magnet excitation for 2-D scan profile, yielding a simple yet low-power drive. Scan angle, mirror size and operation frequency of the presented device allows 30 Mpixel/s addressibility for a 2-D retinal scanning display (RSD). The structural material of the device is single crystalline silicon (SCS) and implementation is done through standard MEMS fabrication processes. Important features of the retinal scanning displays are outlined in Sections II. III describes the display operation and benefits of the actuation technique used in the proposed device. Section IV gives a brief information on device realization. In Section V, equations of motion will be obtained through energy methods. Finite element analysis and electrical equivalent modeling of the microscanner is supplied in this section as well. In Section VI, experimental results and compatibility of the FEA and analytical models with the measurements are discussed. Finally, in Section VII concluding remarks are supplied. II. SYSTEM DESCRIPTION The basic concept of a scanned beam display is shown in Fig. 1. The beam from the light source is sent to the MEMS scanner and focused onto an intermediate image plane with collection optics. The position of this focus point is determined by the angle of the scanning mirror. During the operation, the mirror is scanned biaxially, creating a 2-D pattern onto the intermediate image plane [4]. A set of relay optics is used to relay

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this image pattern onto the viewer’s eye. The focused spot position on the retina is a direct function of the biaxial angles of the mirror. Assuming that the aberrations are controlled and the system is only limited by diffraction, the beam spot size is given as [5], [9] (1) , is the focal length, is the diameter where of the exit pupil and is a shape factor which stands for various aperture shapes and illumination conditions. If the scanner serves as the aperture stop of the system, number of resolvable spots is then found to be

(2) is mechanical zero-to-peak angle, and is opwhere tical full range scan angle. In addition to (2), other factors, such as mirror overscan and incoming beam angle have to be taken into account for a more precise resolution calculation for dis, the product of plays. Along the horizontal scan frequency is the most important performance measure of scanner based displays, as it determines the display resolution along the horizontal axis. The ratio of horizontal scan frequency to display refresh rate determines the vertical display lines. Illustrafor two extreme cases QVGA (320 tive numbers of 240) and HDTV (1280 720) can be given as 16 at 8 at 36 kHz, respectively. kHz and 100 In order to form the rectangular image, the mirror is deflected horizontally at a high-frequency and vertically at the desired refresh rate. The horizontal scan is sinusoidal and bidirectional. The drive frequency is chosen to be at the horizontal resonant frequency of the mirror. The vertical scan is a unidirectional ramp at 60 Hz, which is well below the vertical resonant frequency of the mirror. III. OPERATION OF BIAXIAL MAGNETIC SCANNER Operation of the biaxial scanner depends heavily on superimposing the drive torques of the slow and fast scan directions. The superimposed torque is applied at 45 relative to the two orthogonal scan axes. This approach uses Lorentz’s force excitation of the scanner, created by an external magnetic field and a current carrying coil [8], [10]. Fig. 2(a) shows the layout of the scanner, where a suspended outer frame with a multi turn spiral coil and an inner mirror (scan mirror) attached to the outer frame through fast scan flexures can be identified. As shown in Fig. 2(a), slow (vertical) scan is performed about -axis and fast (horizontal) scan is realized about -axis. The external field is produced by an off-chip permanent magnet. The out of plane force acting on a current carrying conductor is given as [12]

(3)

Fig. 2. (a) Schematic of the biaxial microscanner. The outer frame is connected to the silicon substrate through the slow-scan flexures. In the figure only two turns of the actuation coil are shown for simplicity. Direction of the forces at points a and b are into the paper plane, at points c and d are out of the paper plane. (b) Mechanical schematic of the outer frame-mirror coupled system. (c) Biaxial MEMS scanner die photo.

where is the current running through a closed path of and is the external magnetic field. Since the coil drive current forms a loop on the gimbal, the current direction is reversed across the scan axes. This means the Lorentz forces also reverse sign across the scan axes, resulting in a torque normal to the external magnetic field. This combined torque produces responses in the

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two scan directions depending on the frequency content of the torque. The torque about axis can be approximated as

(4) where is the number of coil turns, is the coil current, is the pitch between the coil turns, is the side length of first coil turn on the short side of frame and is the side length of first coil turn on the long side of frame, respectively. The first term in the summation component of (4) stems from the Lorentz force, the second term stands for the torque arm. Acknowledging that the torque arm and coil side lengths interchange between each other for different axes, magnitude of the actuation torques around and axes are the same. In order to calculate the torque about axis, the first and the second terms of the summation are interchanged. The mirror diameter and scan angles, along with the scan frequency, are chosen as design parameters for obtaining the desired resolution requirements of the display, as indicated by (1). A vertical refresh rate of 60 Hz with a 600 line (SVGA) display, the horizontal scan rate must exceed 18 kHz. Additionally, the spot size has to be small enough for the desired resolution, dictating a mirror flatness requirement. The mirror is designed to keep the dynamic deformation within 1/10 of the wavelength of the scanned beam. In order to eliminate undesirable image artifacts, the vertical mirror motion is required to be a linear ramp. This means the vertical drive must provide sufficient torque to allow non-resonant actuation. Since the maximum torque must be applied at the extremes of angular deflection, pulse drive methods, such as the electrostatic comb drive often used in MEMS devices, are not suitable. It is desirable to avoid the relatively high voltages required for electrostatic actuation, so this type of drive is not suitable for this application. Other commonly used drive mechanisms, such as parallel plate electrostatic, comb-drive, or electromagnetic require small gaps, which interfere with the flow-field of the mirror, reducing the -factor. Another advantage to this structure is not having any electrical conductors running through the fast scan flexures, which can create fatigue and stress problems. Additionally, the scanner assembly should be small and inexpensive to produce, which means that reducing torque requirements by vacuum packaging is undesirable. Sufficiently high factor can be obtained without requiring vacuum packaging, yielding low cost products. For the horizontal (fast) scan, operation at atmospheric pressure produces high damping. A high drive torque is required to overcome this damping. For the vertical drive, the nonresonant operation demands a high torque to overcome the torsional flexure stiffness. This stiffness cannot be set very low due to requirements for shock and handling robustness. The suspended mass cannot be reduced due to mirror size and dynamic flatness requirements. A magnetic drive produces the necessary high torques over the large scan angles needed to achieve the desired operation of both scan axes. The slow scan motion of the scanner is performed by the net torque produced by the forces at points and . The fast scan

Fig. 3. Packaged die assembly of the scanner and integrated position sensor.

is performed by exciting the outer frame in rocking motion, by utilizing the out-of-plane, out-of-phase forces at points and . This motion is coupled to the inner mirror and amplified by the high mechanical quality factor of the mirror resonance. As can be seen from (4), it is possible to properly excite both scan axes with only one applied drive mechanism. The frequency components of the applied torque are selected to excite the horizontal mirror resonance (21.3 kHz) and to provide a ramp drive for the vertical mirror motion. The frequency response characteristics of the mirror and gimbal respectively act as a band-pass filter and a low-pass filter to separate the torque components into their respective motions. Resonant response modes of the scanner are shown in Fig. 4. The vertical resonant (slow-scan) mode and the horizontal mirror (fast-scan) resonant mode are shown in Fig. 4(b) and (d). Note that fast scan mode includes a counter-rotation of the gimbal ring with respect to the mirror. This counter-rotation that is excited by the 21.3 kHz drive signal component. Detailed analytical and experimental results about the frequency spectrum of the scanner modes will be given in Sections V and VI. It is worth noting that since the operation of this device relies on separation of torques about - and -axes, it would not work as a 2-D pointing mirror for arbitrary rotations. IV. REALIZATION A picture of the scanner, highlighting the single drive coil on the outer gimbal, along with the vertical and horizontal torsional flexures, is shown in Fig. 3. The scanner is produced using standard bulk MEMS fabrication techniques. All silicon features are formed from the starting wafer’s single crystal structure. This results in extremely robust structures and highly reliable operation even at large scan angles. The die incorporates two integrated piezoresistive position sensors, one for each axis, and the full die assembly includes a bottom protective cover [6]. The resulting assembly is easy to handle and assemble with very few interconnects required. The drive itself only requires two connections to drive both scan axes. The remaining interconnects provide bias for the integrated position sensors for each axis. These sensors are very

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and are rotational mass moment of inertias for where , the mirror torsion mode, outer frame rocking mode and the outer frame torsion mode. includes moment of inertias of both the outer frame and the scan mirror about the slow scan axis. Effective values of can be calculated using tabulated formulas [9]. Potential energy term comes from the energy stored in the springs

(8) where is the torsional spring constant of the mirror, is the is the spring constant of the outer frame rocking mode and spring constant of the outer frame torsion mode, as illustrated in Fig. 4. Substituting (7) and (8) into (5) results in

Fig. 4. FEA simulations of the mechanical modes of the 2-D scanner. (a) Points 1–3 shown on the layout. (b) Torsion mode of the outer frame (slow scan). (c) Rocking mode of the outer frame in-phase with the mirror. (d) Rocking mode of the outer frame out-of-phase with the mirror (fast scan).

(9) Introducing damping terms, that are linearly dependent on an, to the right-hand side of (6), and substigular velocity as , , and , following equations can tuting be derived: (10a)

precise, allowing for the accurate scan angle control required of high-performance displays. V. MECHANICAL ANALYSIS AND ELECTRICAL EQUIVALENT CIRCUIT In this section, for the magnetically actuated scanner system, equations of motion will be obtained via the Euler–Lagrange (E–L) method. An equivalent schematic describing the parts of the system to be modelled is given in Fig. 2(b). In this figure, a scan mirror is suspended with a torsional spring to a frame, which moves both about its own torsional axis and fast-scan axis. A convenient way of obtaining equations of motion is to use E–L method, where potential and kinetic energies for each component in the system is inspected. Defining the Lagrangian as (5) where and are the kinetic and potential energies, respectively, one can write the equations of motion as follows:

(6)

(10b) (10c) where is the viscous damping factor. In this model, damping factors are used as a parameter to fit the simulation data with the experimental results. Equations (10a)–(10c) include time derivatives of the variables , and . Defining intermediate variables as , , and , we can represent , the equations of motion in the frequency domain in order to construct a transfer matrix between effort variables (force and torque) and flow variables (velocity)

(11) This notation resembles with the -parameter set definition of a linear time invariant three-port electrical network (12a) (12b) (12c)

For the system sketched in Fig. 2(b), three variables are chosen as , and . Assuming a linear system, total kinetic energy, stemming from the inertial forces on the mirror and the outer frame, is

where the reciprocity of the system can be observed from the ). Solution of (11) is matrix (i.e.

(7)

(13)

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Fig. 5. Electrical equivalent of the mechanical system. The loop on the lefthand side stands for the scanner mirror and the one on the right-hand side stands for the outer frame actuator. Component values are obtained using the geometry of the device through tabulated calculations [9].

where is the column vector representing the angular veis the -parameter matrix of the 3-port electrolocities, is the torque vector. mechanical system and An electrical equivalent circuit of the mechanical system can be constructed through the analogy between the mechanical and electrical domains. Starting point for this effort is the matrix notation of the system given (11). Choosing the effort and the flow as the torque and the angular velocity, electrical voltage is mapped to the force and similarly electrical current is mapped to the velocity. If a T-type coupling network is chosen as shown in Fig. 5, then each loop can be used to represent the corrematrix. Each loop in the equivalent circuit sponding row of will have a series resonator circuit as an electrical equivalent to the mechanical spring-mass-damper model. Coupling between these loops is done through the compliance of the mirror torsional spring. Inductors are used to emulate mass or moment of inertia, capacitors for compliances and resistors for damping conlosses. The branch containing elements of , , and ducts the current of and models the slow-scan motion of the scanner. Since the torsional motion of the outer frame does not have any effect on the fast-scan motion, no coupling is used between the slow-scan and fast scan loops. The rocking mode of , and and couthe outer frame is modelled with , pled to the torsion mode of the mirror ( , and ) by a T-shaped capacitor network. SPICE simulation of the described equivalent circuit is presented in Fig. 6. This plot represents the frequency spectrum of the points 1–3, previously shown in Fig. 4(a). The slow scan resonance, associated with the torsion of the outer frame, occurs at 400 Hz. This mode of the outer frame is followed by the mirror and used for vertical scan operation at the refresh rate of 60 Hz. Refresh rate is chosen to be around the skirt of the resonance peak, yet the actuation toque is sufficient to create large angular displacements. The resonance at 4 kHz belongs to a mode where the outer frame and the mirror are moving in-phase. The outer frame is in the rocking mode which is translated into the torsion of the mirror. This mode is not used in the operation of the scanner for display applications. The fast scan resonance, modelled by the mirror torsion box in Fig. 5 appears at 21.3 kHz. The large ratio between the angular rotations of point 1 and point 2 at this resonance proves the concept of the mechanical coupling. Essentially, a small rocking displacement of the outer frame is band-pass filtered, phase shifted and -times amplified at the

Fig. 6. SPICE simulation of the equivalent circuit given in Fig. 5.

resonance frequency to give peak scan angle. This mode does not respond significantly to the low frequency components of the drive torque, so the resulting scan motion is pure sinusoidal motion at the resonant 21.3 kHz frequency. Spectrum of point 2 presents a zero around 21.2 kHz stemming from the coupling between the outer frame and the mirror. The origin of this mechanical zero can be understood from (11), which defines the transfer function between the angular rotation and the respective drive torque of point-2. The location of the element of the matrix, which constitutes zero is outlined by the nominator of the transfer function of point-2. The frequency response of vertical (slow) scan mode greatly attenuates the 21.3 kHz component as can be seen by the frequency spectrum of point-3 in Fig. 6. However, the lower frequency drive components of the vertical ramp do effectively drive the slow-scan mode motion. Even frequency components as high as 2 kHz still have enough gain to affect the scanner’s motion. This is important for producing a high fidelity linear ramp profile. In summary, the scanner mechanism acts as a high- mechanical filter, separating the superimposed drive torque into its component parts. This allows for biaxial scan control with only one applied drive force mechanism. VI. MEASUREMENTS Scanner frequency response is characterized using the setup shown in Fig. 7. The setup consists of a laser Doppler vibrometer (LDV), a function generator and an oscilloscope. Communication between the oscilloscope and the function generator is accomplished by GPIB interface. LDV sends a laser beam to the section of interest and measures the Doppler shift of the returning beam to give an voltage at its output. In the experiments, both coil excitation voltage (current) and the LDV output

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Fig. 7. Gain-phase analyzer setup used in extraction of the transfer function. Data collection PC controls the function generator and the oscilloscope, through a custom MATLAB program, to obtain magnitude and phase values simultaneously as the frequency of the input signal is swept.

voltage are sinusoidal signals. For a given setting of the LDV, output voltage is converted to velocity by scaling it with a con, position stant. Assuming a peak-to-peak displacement of and velocity of an arbitrary spot on the scanner in time domain is given as

(14a) (14b) corresponds to peak-to-peak velocity. Equation where (14b) is the counterpart of the LDV output. Thus, for a given sinusoidal excitation, by finding the peak velocity and the phase of the LDV output for each frequency step, one can obtain the transfer function of the scanner in terms of gain-phase plots. Characterization of the scanner is executed in the ambient air, at three locations on the device shown as points 1–3 in Fig. 4(a). Due to the high mechanical quality factors of the device, the input excitation is kept small around the resonance peaks. This avoids the saturation of the LDV output and results in reliable measurements. The overall spectrum is a combination of rotation angles normalized to the input excitation. Fig. 8 shows the normalized rotation angles as a function of frequency for points 1–3 on the scanner. Point 1 is a location on the mirror and therefore does not exhibit any motion around slow-scan resonance (400 Hz). Two main peaks associated with this point are at 4 and 21.3 kHz. The latter one corresponds to the fast scan operation, where the outer frame moves in the rocking mode meanwhile the mirror is in the torsion mode with a relative phase difference of 180 . The angular motion of point 2 is essentially amplified by the -factor of the mirror and translated into mirror torsion. The spectrum of point 2 features a valley around 21.2 kHz, just before the fast scan resonance. This mechanical zero is the signature of the coupling between the outer frame and the mirror. The outer frame displacement is under substantial attenuation, which can physically be explained as the outer frame transferring all of its energy to the mirror. One important property of this coupled system is that there are no drive components or features near the

Fig. 8. Frequency spectrum of angles of the three locations on the device. (a) DC-to-22 kHz spectrum. (b) 20.8 kHz-to-21.5 kHz spectrum showing the poles and zeros associated with the fast scan operation.

mirror. This results in reduced gas damping a higher mechanical quality factor for the mirror. Any displacement of point 2 in the rocking mode will be amplified by the mirror quality factor and converted into torsion of the mirror. Low actuation of forces, created by the low excitation signal (coil power) can effectively drive the mirror to create large angular displacements, factors. The torsional resonance mode of the therefore high outer frame about slow-scan axes is designated to appear around 400 Hz as can be seen from the curve of point 3 in Fig. 8. As discussed before, the scanner is driven at the off-resonant frequency of 60 Hz to implement vertical display refresh. The measurement setup depicted in Fig. 7 allows detection of rotation angles with a high dynamic range ( 106 dB), in the to 1 deg/mA with the proper excitation range of 5 signals. Transient response of the vertical scan angle and superimposed drive current are shown in Fig. 9. The plot in the lower left shows the composite drive current for both the vertical and horizontal axes. Only the envelope of the 21.3 kHz component is visible in this time scale. The plot in the upper left shows the resulting vertical scan angle amplitude response. The two plots on the right show magnified views of the retrace scan portion of these two left hand plots. The lower right plot

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Fig. 9. Transient behavior of the vertical scan angle and superimposed drive current. Fig. 11. Comparison of the scanners published in the literature.

operation on resonance, is able to achieve 58 optical scan angle with decreasing drive efficiency. These high scan angles are made possible by the high drive torque capabilities of the new bimagnetic drive design, by the careful design of stresses throughout the torsional flexures, and by careful control of the quality of the etched surface side walls. Based on our current MEMS scanner design and fabrication capabilities, it is now possible to make a scanner meeting the requirements for SXGA (1280 1024) resolution retinal scanning displays. VII. CONCLUSION

Fig. 10. Slow and fast scan optical angles as a function of coil drive current.

clearly shows the superimposed 21.3 kHz horizontal drive component, while the upper right plot shows how the slow scan responds to this composite drive current. Notice that there is very little 21.3 kHz component visible on the slow scan angular amplitude response curve. The fast scan angular response is a pure 21.3 kHz sinusoidal curve (and is therefore not plotted). As mentioned above, its frequency response to the superimposed lower harmonics is so low that it is not visible in the scan amplitude response at all. for the The plots of Fig. 9 show an optical scan angle of vertical axis. Scanners have been tested using bimagnetic actuation to much greater angles. Fig. 10 shows the optical angles of fast-scan and slow-scan as a function of the drive current. The slow-scan frequency response exhibits a linear dependency on the coil current. Fig. 10 shows the fast and slow scan optical scan angles as a function of drive current. Due to the off-resonance operation, the slow scan axis is relatively linear with drive current up to 65 scan angle. The fast scan axis, with the benefit of -amplified

A new drive mechanism has been developed to meet the needs of high performance raster scanning mirrors. Using a simple electro-magnetic drive it is possible to achieve high frequency scanning in one axis and a fully linear sawtooth ramp in the other axis all in ambient air operation. The one-atmosphere operation eliminates the need for a glass cover on the package, improving system performance while lowering fabrication costs. As a result of the simplification in packaging allowed by this design, the high performance of this scanner can be achieved at very low cost. Fig. 11 compares the scanners published in the literature, product and scan frequency [9], [11], [13], according to [15]–[24]. As seen from Fig. 11, the scanner presented in this paper is far superior in performance compared to others available in the literature and incorporates two-axis operation and integrated position sensors on both axis. This design encompasses the desired goals. • Two axes of the scanner are driven from one magnetic field and one current drive loop. • Scanner mechanical dynamics separate the drive harmonics to create the desired mechanical response. • Actuation mechanism results in high torque drive on both axes allows one-atmosphere fast scan operation as well as dc to 2 kHz actuation of slow scan axis over entire scan angle.

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• Realized device is a high performance two-axis scanner design with an integrated on-chip position sensor. • This novel drive concept makes it possible to develop scanners capable of supporting SXGA displays without vacuum packaging and with linear-ramp slow-scan operation. This new scanner actuation mechanism has already been introduced into Microvision’s production NOMAD Expert Technician System Head-Worn Display. ACKNOWLEDGMENT The authors would like to thank W. Davis of Microvision Corp. for helping in the mechanical analysis of the device. Ç. Ataman of Koç University is also thanked for his assistance in automation of the characterization setup. REFERENCES [1] H. Urey, D. Wine, and T. Osborn, “Optical performance for MEMSscanner based microdisplays,” in Proc. SPIE, MOEMS Miniaturized Systems, 2000, vol. 4178, pp. 176–185. [2] H. Urey, D. Wine, and J. R. Lewis, “Scanner design and resolution tradeoffs for miniature scanning displays,” in Proc. SPIE Flat Panel Display Technology and Display Metrology, San Jose, CA, Jan. 1998, vol. 3636, pp. 60–68. [3] D. Wine, M. P. Helsel, L. Jenkins, H. Urey, and T. D. Osborn, “Performance of a bi-axial MEMS-based scanner for microdisplay applications,” in Proc. SPIE, 2000, vol. 4178, pp. 186–196. [4] R. B. Sprague, T. Montague, and D. Brown, “Bi-axial magnetic drive for scanned beam display mirrors,” in Proc. SPIE, MOEMS Display and Imaging Systems III, 2005, vol. 5721, pp. 1–13. [5] L. Beiser and R. B. Johnson, Handbook of Optics, 2nd ed. New York: McGraw-Hill, 1995, pt. II. [6] D. E. Fulkerson, “A silicon integrated circuit force sensor,” IEEE Trans. Electron Dev., vol. ED-16, no. 10, pp. 867–870, Oct. 1969. [7] H. Miyajima, N. Asaoka, M. Arima, Y. Minamoto, K. Murakami, K. Tokuda, and K. Matsumoto, “An electromagnetic optical scanner with polyamide-based hinges,” in Proc. IEEE Transducers’99, Sendai, Japan, 1999, pp. 372–375. [8] H. Miyajima, N. Asaoka, M. Arima, Y. Minamoto, K. Murakami, and K. Matsumoto, “A durable, shock-resistant electromagnetic optical scanner with polyimide-based hinges,” J. Microelectromech. Syst., vol. 10, no. 9, pp. 418–424, Sep. 2001. [9] H. Urey, “Torsional MEMS scanner design for high-resolution display systems,” in Proc. SPIE, Optical Scanning II, Seattle, WA, Jul. 2002, vol. 4773, pp. 27–37. [10] L. Houlet, G. Reyne, T. Iizuka, T. Bourouina, E.-D. Gergam, and H. Fujita, “Copper microcoil arrays for the actuation of optical matrix microswitches,” in Proc. SPIE, 2001, vol. 4592, pp. 422–428. [11] H. Urey, F. DeWitt, IV, and S. Luanava, “Optical scanners for highresolution RSD systems,” in Proc. SPIE, Head and Helmet Mounted Displays VI, Orlando, FL, 2002, vol. 4711. [12] M. N. O. Sadiku, Elements of Electromagnetics, 3rd ed. Oxford, U.K.: Oxford Univ. Press, 2001. [13] H. Urey and C. Ataman, “Modeling and characterization of comb actuated resonant microscanners,” J Micromech. Microeng., vol. 16, no. 1, pp. 9–16, Jan. 2006. [14] U. Hofmann, S. Muehlmann, M. Witt, K. Dorschel, R. Schutz, and B. Wagner, “Electrostatically driven micromirrors for a miniaturized confocal laser scanning microscope,” in Proc. SPIE, Miniaturized Systems With Micro-Optics and MEMS, 1999, vol. 3878, pp. 29–38. [15] H. Schenk, P. Durr, D. Kunze, H. Lakner, and H. Kuck, “An electrostatically excited 2-D-micro-scanning-mirror with an in-plane configuration of the driving electrodes,” in Proc. IEEE MEMS, 2000, vol. 13, pp. 473–478. [16] H. Schenk, P. Durr, T. Haase, D. Kunze, U. Sobe, H. Lakner, and H. Kuck, “Large deflection micromechanical scanning mirrors for linear scans and pattern generation,” IEEE J. Sel. Topics Quantum Electron., vol. 6, no. 5, pp. 715–722, Sep. 2000.

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[17] Y. C. Ko, J. W. Cho, H. G. Jeong, W. K. Choi, Y. K. Mun, J. H. Lee, and J. H. Lee, “Design and fabrication of eye-type scanning mirror with dual vertical combs,” in Proc. IEEE-LEOS Conf. Optical MEMS 2004, Takamatsu, Japan, 2004, pp. 184–185. [18] M. Tani, M. Akamatsu, Y. Yasuda, H. Fujita, and H. Toshiyoshi, “A 2D-optical scanner actuated by PZT film deposited by Arc Discharged Reactive Ion-Plating (ADRIP) method,” in Proc. IEEE-LEOS Conf. Optical MEMS 2004, Takamatsu, Japan, 2004, pp. 188–189. [19] D. Dickensheets and G. KiNo, “Microfabricated biaxial electrostatic torsional scanning mirror,” in Proc. SPIE, 1997, vol. 3009, pp. 141–150. [20] F. Filhol, E. Defay, C. Divoux, C. Zinck, and M.-T. Delaye, “Piezoelectric micromirrors for fast optical scanning with large angular deflection,” in Proc. IEEE-LEOS Conference Optical MEMS 2004, Takamatsu, Japan, 2004, pp. 190–191. [21] S. Schweizer, P. Cousseau, G. Lammel, S. Calmes, and P. Renaud, “Two-dimensional thermally actuated optical microprojector,” Sensors Actuators A, vol. 85, pp. 424–429, 2000. [22] K. Torashima, T. Teshima, Y. Mizoguchi, S. Yasuda, T. Kato, Y. Shimada, and T. Yagi, “A micro scanner with low power consumption using double coil layers on a permalloy film,” in Proc. IEEE-LEOS Conf. Optical MEMS 2004, Takamatsu, Japan, 2004, pp. 192–193. [23] H. Schenk, P. Durr, D. Kunze, H. Lakner, and H. Kuck, “A resonantly excited 2d-micro-scanning-mirror with large deflection,” Sensors Actuators A, vol. 89, pp. 104–111, 2001. [24] H. Miyajima, “Development of a MEMS electromagnetic optical scanner for a commercial laser scanning microscope,” J. Microlithogr. Microfabrication, Microsyst., vol. 3, no. 2, pp. 348–357, 2004. [25] H. Urey, A. D. Yalcinkaya, T. Montague, D. Brown, R. Sprague, O. Anac, C. Ataman, and I. Basdogan, “Two-axis MEMS scanner for display and imaging applications,” in Proc. IEEE Optical MEMS Conf., Oulu, Finland, 2005, pp. 17–18. Arda D. Yalcinkaya received the B.S.E.E. degree from the Electronics and Telecommunication Engineering Department, Istanbul Technical University, Istanbul, Turkey, the M.Sc. and Ph.D. degrees from theTechnical University of Denmark (DTU), Mikroelektronik Centret, Kgs. Lynby, Denmark, all in electrical engineering, in 1997, 1999, and 2003, respectively. Between 1999 and 2000, he was a Research and Development Engineer at Aselsan Microelectronics, Ankara, Turkey. He had short stays as a Visiting Reseacher at Interuniversity Microelectronic Center (IMEC), Leuven, Belgium, and Centro Nacionale de Microelectronica (CNM), Barcelona, Spain, in 2000 and 2003. Since 2003, he has been a research associate at Koç University, Istanbul, Turkey, where he is engaged with start up of a cleanroom facility. He is also working as a part-time ASIC Designer for Microvision Inc., Seattle, WA. His research interests include design, fabrication and characterization of MEMS, CMOS-MEMS integration, nanotechnology and design of analog ASICs. He was a Sabanci Foundation (VAKSA) scholar between 1992 and 1997, and a Turkish Education Foundation (TEV) scholar between 1997 and 1999.

Hakan Urey received the B.S. degree from Middle East Technical University, Ankara, Turkey, in 1992, and M.S. and Ph.D. degrees from the Georgia Institute of Technology, Atlanta, in 1996 and in 1997, respectively, all in electrical engineering. He is currently an Assistant Professor at Koç University, Istanbul, Turkey, where he has been seince 2002. He joined Microvision Inc., Seattle, WA, in 1998. He has published more than 50 journal and conference papers, five edited books, two book chapters, and he has nine issued and several pending patents. His research interests are generally in the area of information optics and microsystems, including micro-optics, optical system design, microelectromechanical systems (MEMS), and display and imaging systems. Dr. Urey is a member of SPIE, OSA, and IEEE-LEOS, and Vice-President of the Turkey chapter of IEEE-LEOS. He is the Chair of Photonics West MOEMS Display and Imaging Systems Conference and Photonics Europe Symposium MEMS, MOEMS, and Micromachining Conference.

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Dean Brown received the B.S. degree in mechanical engineering from the University of California, Santa Barbara, in 1974. His experience includes mechanical engineering analysis and design in a wide variety of industries, including electronics, ocean engineering, nuclear power generation, hazardous materials handling, and transportation. He has spent the last nine years designing and analyzing MEMS devices, and is currently a Principal Engineer for Microvision, Inc., Seattle, WA, performing MEMS optical scanner design and analysis.

Tom Montague received the B.S. degree in aeronautical and astronautical engineering and the M.Sc. degree in physics, both from the University of Washington, Seattle, in 2000 and 2005, respectively. Over the past nine years, he has worked as a Research and Development Engineer of laser scanning instruments and display systems. From 1996 to 1999, he worked for Laser Sensor Technology, Redmon, WA, developing laser- based particle size measurement systems for applications ranging from the monitoring of cell growth to petroleum processing and for operating environments from cryogenic to high temperature. Since 2000, he has been with Microvision Inc., Seattle WA, USA where he is currently the Manager of the MEMS design group. He has developed two generations of the MEMS scanners used in Microvision’s display products.

Randy Sprague, photograph and biography not available at the time of publication.